The TARDIS, with the Doctor, Ian, Susan and Barbara on board, materialises beside the River Thames in the year 2167. The world to which they emerge, however, is eerily silent and signs of decay are rife. They soon discover that the streets are patrolled by zombie-like humans, flying saucer-like craft occupy the skies and that desperate rebels are hiding below ground in the disused Underground system. But worse is still to come!

The Daleks, thought destroyed by the Doctor, have invaded and enslaved humanity, having first bombarded it with cosmic storms. Why have the Daleks chosen Earth in particular? What is the significance of the giant mine in Bedfordshire to which they are shipping human slaves? And can the Doctor unite with the small band of resistance fighters to stop the Daleks before their plans wreck havoc with the Earth forever?